ovl: create ovl_need_index() helper

The helper determines which lower file needs to be indexed
on copy up and before nlink changes.

For index=on, the helper evaluates to true for lower hardlinks.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -536,11 +536,7 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
 {
 	int err;
 	struct ovl_fs *ofs = c->dentry->d_sb->s_fs_info;
-	bool indexed = false;
-
-	if (ovl_indexdir(c->dentry->d_sb) && !S_ISDIR(c->stat.mode) &&
-	    c->stat.nlink > 1)
-		indexed = true;
+	bool indexed = ovl_need_index(c->dentry);
 
 	if (S_ISDIR(c->stat.mode) || c->stat.nlink == 1 || indexed)
 		c->origin = true;

fs/overlayfs/overlayfs.h

@@ -241,6 +241,7 @@ void ovl_clear_flag(unsigned long flag, struct inode *inode);
 bool ovl_test_flag(unsigned long flag, struct inode *inode);
 bool ovl_inuse_trylock(struct dentry *dentry);
 void ovl_inuse_unlock(struct dentry *dentry);
+bool ovl_need_index(struct dentry *dentry);
 int ovl_nlink_start(struct dentry *dentry, bool *locked);
 void ovl_nlink_end(struct dentry *dentry, bool locked);
 int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir);

fs/overlayfs/util.c

@@ -463,6 +463,23 @@ void ovl_inuse_unlock(struct dentry *dentry)
 	}
 }
 
+/*
+ * Does this overlay dentry need to be indexed on copy up?
+ */
+bool ovl_need_index(struct dentry *dentry)
+{
+	struct dentry *lower = ovl_dentry_lower(dentry);
+
+	if (!lower || !ovl_indexdir(dentry->d_sb))
+		return false;
+
+	/* Index only lower hardlinks on copy up */
+	if (!d_is_dir(lower) && d_inode(lower)->i_nlink > 1)
+		return true;
+
+	return false;
+}
+
 /* Caller must hold OVL_I(inode)->lock */
 static void ovl_cleanup_index(struct dentry *dentry)
 {
@@ -533,11 +550,11 @@ int ovl_nlink_start(struct dentry *dentry, bool *locked)
 
 	/*
 	 * With inodes index is enabled, we store the union overlay nlink
-	 * in an xattr on the index inode. When whiting out lower hardlinks
+	 * in an xattr on the index inode. When whiting out an indexed lower,
 	 * we need to decrement the overlay persistent nlink, but before the
 	 * first copy up, we have no upper index inode to store the xattr.
 	 *
-	 * As a workaround, before whiteout/rename over of a lower hardlink,
+	 * As a workaround, before whiteout/rename over an indexed lower,
 	 * copy up to create the upper index. Creating the upper index will
 	 * initialize the overlay nlink, so it could be dropped if unlink
 	 * or rename succeeds.
@@ -545,8 +562,7 @@ int ovl_nlink_start(struct dentry *dentry, bool *locked)
 	 * TODO: implement metadata only index copy up when called with
 	 *       ovl_copy_up_flags(dentry, O_PATH).
 	 */
-	if (ovl_indexdir(dentry->d_sb) && !ovl_dentry_has_upper_alias(dentry) &&
-	    d_inode(ovl_dentry_lower(dentry))->i_nlink > 1) {
+	if (ovl_need_index(dentry) && !ovl_dentry_has_upper_alias(dentry)) {
 		err = ovl_copy_up(dentry);
 		if (err)
 			return err;